High-strength films of block copolymer latices

ABSTRACT

An aqueous dispersion is claimed which is capable of forming a free-standing, coherent, elastomeric, solid film which, after drying and annealing at 80° C. for 30 minutes, demonstrates a tensile strength of about 11.0 MPa or greater wherein the dispersion comprises: I. an organic phase comprising: (a) one or more block copolymer(s) corresponding to the formula A-B-X m  -(B-A) n , wherein each A polymer block consists essentially of a monovinylidene aromatic monomer, having a weight average molecular weight from about 8,000 to about 15,000 Daltons, each B polymer block consists essentially of a conjugated diene and, optionally, a monovinylidene aromatic monomer having a weight average molecular weight from about 30,000 to about 200,000 Daltons, X is the remnant of a multifunctional coupling agent, m is 0 or 1, and n is an integer from 1 to 5, and (b) optionally, an extender for the block copolymer which is compatible with the B block; II. a surfactant; and III. water, wherein the A block effective phase volume in the organic phase is from about 5 to about 20 percent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.08/326,635, filed Oct. 20, 1994, now abandoned, which is a divisional ofSer. No. 08/170,625, filed Dec. 20, 1993, now abandoned, which is acontinuation-in-part application of application Ser. No. 08/002,433,filed Jan. 8, 1993, now abandoned (all incorporated herein byreference).

BACKGROUND OF THE INVENTION

The present invention relates to high-strength films prepared fromaqueous dispersions of block copolymers of vinyl aromatic monomers andconjugated dienes.

Block copolymers of the conventional A-B-A type form strong films whencast from solutions in organic solvents. The use of aqueous dispersionsor latices to form films or articles of intricate design is preferred tothe use of casting from solutions because no objectionable fumes arereleased during the drying step. However, films of comparable thicknessprepared by casting from their aqueous dispersions or latices aregenerally weak. To improve the strength of such films, U.S. Pat. No.3,360,599 taught the use of an annealing procedure. Disadvantageously,this annealing procedure requires elevated temperatures and/or longannealing times. As a consequence, the resulting films often haveinferior strength properties, due to polymer degradation, and/or thetime required for film formation is unacceptably long. U.S. Pat. No.4,199,490 taught the addition of a second aqueous dispersion comprisinga rubber, synthetic resin or a mixture thereof to enable the formationof films upon drying at room temperature. In the absence of suchadditive, the block copolymer dispersion did not possess adequatefilm-forming properties at moderate or low temperatures. In U.S. Pat.No. 3,238,173, there was disclosed the preparation of concentratedaqueous dispersions by contacting the dilute latex with an aliphatichydrocarbon that is a non-solvent for the non-elastomeric block,removing the hydrocarbon and concentrating the latex. The use of suchnon-solvents is undesirable, due to the added complexity of the processand the presence of residual organic contaminants in the resultingfilms.

Accordingly, there remains a need to provide films prepared from aqueousdispersions of block copolymers having improved strength properties. Inaddition, it would be desirable to provide a process capable ofpreparing strong films from aqueous latices of block copolymers thatuses relatively short times and mild temperature conditions for theannealing step to thereby avoid significant polymer degradation.Finally, it would be desirable to provide a process for the preparationof thin elastomeric articles by film deposition from a block copolymerlatex that avoids the use of additives.

Many thin elastomeric articles are prepared using coagulation dippingtechniques. It is desirable to prepare films from latices of aqueousdispersions of block copolymers using coagulation dipping techniques.What is needed are stable aqueous dispersions of block copolymers whichform good films by coagulation wherein the films anneal rapidly atmoderate temperatures and demonstrate high tensile strengths.

For many uses, thin elastomeric films must demonstrate resistance todegradation by ozone. What is needed are stable aqueous dispersions ofblock copolymers which form ozone-resistant films, and suchozone-resistant films.

SUMMARY OF THE INVENTION

Accordingly, the present invention comprises an aqueous dispersion whichis capable of forming a free-standing, coherent, elastomeric, solid filmwhich, after drying and annealing at 80° C. for 30 minutes, demonstratesa tensile strength of about 11.0 MPa or greater wherein the dispersioncomprises:

I. an organic phase comprising;

(a) one or more block copolymer(s) corresponding to the formula

    A-B-X.sub.m -(B-A).sub.n

wherein each A is a polymer block consisting essentially of amonovinylidene aromatic monomer, each B is a polymer block consistingessentially of a conjugated diene and, optionally, a monovinylidenearomatic monomer, X is the remnant of a multifunctional coupling agent,m is 0 or 1, and n is an integer from 1 to 5, each monovinylidenearomatic monomer block, A, having a weight average molecular weight fromabout 8,000 to about 15,000 Daltons, each conjugated diene block, B,having a weight average molecular weight from about 30,000 to about200,000 Daltons, and

(b) optionally, an extender for the block copolymer which is compatiblewith the B block;

II. a surfactant in sufficient amount to emulsify the organic phase inwater and such that a film formed from the dispersion exhibits therequired properties; and

III. water,

wherein the average A block content of the organic phase is from about 5to about 25 percent by weight and the A block effective phase volume inthe organic phase is from about 5 to about 20 percent, wherein theamount of extender present is sufficient to achieve the desired 5effective phase volume of the A block and the required film properties.

In another embodiment, the invention comprises a high-strength,free-standing film comprising the block copolymer described above,optionally, the extender described hereinbefore and a residual amount ofthe surfactant described hereinbefore, wherein the film exhibits atensile strength at break of about 11.0 MPa or greater after annealingat 80° C. for 30 minutes.

In yet another embodiment, the invention comprises a process forpreparing a film which comprises (1) forming an aqueous dispersion fromthe block copolymer, water, extender and surfactant as describedhereinbefore, (2) depositing a layer of the aqueous dispersion on asurface to form a film, (3) removing the film from the surface, and (4)annealing the film under conditions such that the film exhibits tensilestrength at break of about 11.0 MPa or greater after annealing at 80° C.for 30 minutes. The invention also comprises films prepared by theprocess described.

Surprisingly, such block copolymers readily form thin films bydeposition onto solid surfaces from an aqueous dispersion. Such filmsmay be dried to form coherent, elastomeric, solid film articles havinghigh annealed strength properties using short annealing times and mildannealing temperatures. Examples of such articles include surgicalgloves, examination gloves, condoms, catheters, balloons and other thinelastomeric articles. If a tackifier and, optionally, other formulantsknown to one skilled in the art are combined with the block copolymer,films having adhesive properties may also be prepared. Such films may bedeposited onto a thin, flexible substrate for use as pressure sensitivetapes, packaging tapes, masking tapes, labels, etc.

DETAILED DESCRIPTION OF THE INVENTION

It has been discovered that by careful selection of the block copolymerand the total volume of the polystyrene phase, stable aqueousdispersions can be prepared which form strong free-standing films upondrying at relatively low temperatures. In selecting appropriate blockcopolymers, the weight average molecular weight of the monovinylidenearomatic monomer block must be within the limits defined herein. If thechain length is too high, the annealing time required to form ahigh-strength film becomes unacceptably long. If the endblock length istoo low, the films prepared do not exhibit acceptable tensile strengths.The total volume of the monovinylidene aromatic monomer (block A) in theorganic phase is important in that, if the volume of the monovinylidenearomatic monomer phase is too high, stable dispersions cannot be formedusing a relatively low amount of surfactants. If the A block phasevolume is too low, the films prepared from the block copolymers will notexhibit the required tensile strengths.

Both linear and radial block copolymers are suitably employed in theinvention. Most preferably, however, the block copolymers are triblockcopolymers, i.e., n in Formula (I) is equal to 1.

The block copolymers may be partially tapered, fully tapered oruntapered polymers. By the term "tapered" is meant that the B blockchanges gradually from diene-rich or pure diene homopolymer in thecenter to include increasing proportions of monovinylidene aromaticmonomer in a gradual conversion towards the junction of themonovinylidene aromatic block of the block copolymer and terminates inpure homopolymer of the monovinylidene aromatic monomer (the A block).The conversion may be symmetrical or unsymmetrical with respect to thecenter of the B block. Triblock copolymers possessing taperedness atonly one junction are referred to as "half-tapered" polymers.

Preferable monovinylidene aromatic monomers for use herein includestyrene and alkyl-substituted derivatives of styrene. Examples includestyrene, α-methylstyrene, vinyl toluene, etc. A more preferredmonovinylidene aromatic monomer is styrene. Conjugated dienes suitablyemployed in the present invention include 1,3-butadiene, isoprene ormixtures thereof. Preferably, the conjugated diene is isoprene.Preferably, the amount of monovinylidene aromatic monomer in the organicphase is about 5 percent by weight or greater and more preferably, about10 percent by weight or greater. Preferably, the amount ofmonovinylidene aromatic monomer in the organic phase is about 25 percentby weight or less and about 20 percent by weight or less. Preferably,the monovinylidene aromatic monomer block has a weight average molecularweight of about 5,000 Daltons or more and more preferably, 8,000 Daltonsor more. Preferably, the monovinylidene aromatic monomer block has aweight average molecular weight of about 20,000 Daltons or less and morepreferably, 15,000 Daltons or less. Preferably, each conjugated dieneblock (B) has a weight average molecular weight of about 30,000 Daltonsor greater, more preferably, 40,000 Daltons or greater and mostpreferably, 50,000 Daltons or greater. Preferably, each conjugated dieneblock has a weight average molecular weight of 240,000 Daltons or less,more preferably, 200,000 Daltons or less, even more preferably, 120,000Daltons or less and most preferably, 100,000 Daltons or less.Preferably, the monovinylidene aromatic polymer block has an effectivephase volume in the organic phase of about 5 volume percent or greater,more preferably, 10 volume percent or greater, and even more preferably,12 volume percent or greater. Preferably, the monovinylidene aromaticpolymer block has an effective phase volume in the organic phase ofabout 20 volume percent or less, more preferably, 19 volume percent orless, even more preferably, 18.5 volume percent or less and mostpreferably, 18 volume percent or less. "Organic phase" as used hereinrefers to all of the organic-based materials in the dispersion, exceptthe surfactant. Such materials include the block copolymers and anyoptional extender.

A blend of two or more block copolymers may be used in this invention.All of the block copolymers used preferably have A blocks which haveweight average molecular weights in the range of from about 8,000 toabout 15,000 Daltons. The composition weighted average styrene contentof the blended copolymers is preferably from about 5 to about 25 percentby weight. One or more of the components may have a styrene contentoutside of the stated range, provided the average is within the statedrange. In the embodiment wherein one of the block copolymers in such ablend has a styrene content above 25 weight percent, it is preferredthat the styrene content be about 35 weight percent or less and, morepreferably, about 30 weight percent or less. Preferably, the totalamount of block copolymer having a styrene content above about 25percent by weight is about 35 percent by weight or less and, morepreferably, about 30 percent by weight or less. The block copolymers canbe blended in bulk and thereafter emulsified. Optionally, the blockcopolymers may be emulsified separately and the dispersions can beblended. Methods of blending the bulk block copolymers or aqueousdispersions of the block copolymers are well known in the art.

In some embodiments of the invention, the one or more block copolymersmay have an effective phase volume of the A block which is greater thanpreferred. In order to reduce the phase volume of the A block, anextender may be blended with the block copolymer to reduce the effectivephase volume of the A block in the organic phase to the required ordesired level. Extenders useful in the invention are non-volatileorganic materials which are compatible with the B block, that is, suchextenders are soluble in the B block or form a single phase with the Bblock when the extender is mixed with one or more block copolymers.Further, useful extenders do not degrade the properties of the filmsprepared from the aqueous dispersions of the invention such that thetensile strengths are less than 11.0 MPa when the films are annealed at80° C. for 30 minutes. Among preferred extenders are hydrocarbon oils,polymers or oligomers derived from monomers having olefinic unsaturationcompatible with the B block, or mixtures thereof. More preferredextenders are the aliphatic hydrocarbon and naphthenic oils, with themost preferred class of extender oils being the aliphatic hydrocarbonoils. The preferred hydrocarbon oils are selected according to theultimate end use and the cost of such oils. Among preferred oils areTufflo™ 6056 mineral oil (trademark of Atlantic Richfield Company) andShellflex™ 371 mineral oil (trademark of Shell Oil Company). Thepreferred polymers useful as extenders include polyisoprene,polybutadiene, polyisobutylene, polyoctene, polyethylene vinyl acetate,polyethylene methacrylate, ethylene-propylene diene monomer-basedpolymers, styrene-butadiene random copolymers and ethylene-styrenecopolymers. Most preferred polymers include polyisoprene andpolybutadiene. The extenders are present in sufficient amount to achievethe desired effective phase volume of the A block. If too much extenderis used, the films prepared from the aqueous dispersions would not meetthe tensile strengths required. The amount of extender is preferablyabout 45 percent by weight or less of the organic phase, morepreferably, about 40 percent by weight or less and most preferably,about 30 percent by weight or less. If present, the extender is presentin an amount of about 1 percent by weight or greater of the organicphase and more preferably, 5 percent by weight or greater.

The extender oils can be blended with the block copolymer in bulk andthe blend can be emulsified. Alternatively, the extender oils and blockcopolymers can be separately emulsified and the dispersions can beblended to achieve the desired organic phase composition. In yet anotherembodiment, the extender may be added directly to a dispersion of theblock copolymers. Methods of performing such blending are well known inthe art. In the embodiment where the extender is a polymer, the polymeris either blended into a solution of block copolymer in organic solventor into a dispersion of the block copolymer. Preferably, the extender isin the form of an organic solution or dispersion when blended with theblock copolymer.

To achieve the required organic phase composition, a blend of two ormore copolymers and one or more extenders may be used in combination.

Effective phase volume or volume percent of the monovinylidene aromaticmonomer blocks may be less than the weight percent of monovinylidenearomatic monomers in such copolymers. Especially if one or more of thepolymers is tapered, the monovinylidene aromatic monomer blocks are morecompatible and, therefore, more soluble in the diene polymer phase ofthe resulting multiple phase structure compared to pure monovinylidenearomatic homopolymer blocks. Due to such solubility, the volume of thephase segregated monovinylidene aromatic polymer is less than thecontent of such monovinylidene aromatic monomer expressed by weight.Accordingly, the percentage of the monovinylidene aromatic monomer blockin the block copolymer or organic phase, measured as a volume percent,is less than the percentage thereof measured by weight. In order todetermine the volume percent of the monovinylidene aromatic polymerblock, the corresponding weight percentage of monovinylidene aromaticmonomer is divided by a correction factor. The correction factor is avalue equal to the sum of ratios of each monomer's content in weightpercent divided by the respective density of a homopolymer of suchmonomer. For a two-component block copolymer, this may be expressed asfollows:

    %(vol.sub.a)=%(wt.sub.a)/D.sub.a /(%(wt.sub.a)/D.sub.a +%(wt.sub.b)/D.sub.b)                                     (II)

where:

%(vol_(a)) is the effective phase volume in percent for themonovinylidene aromatic polymer block;

%(wt_(a)) and %(wt_(b)) are the respective weight percent contents ofmonovinylidene aromatic monomer and diene monomer in the blockcopolymer; and

D_(a) and D_(b) are the respective densities of homopolymers, themonovinylidene aromatic monomer and diene monomer.

In those embodiments where an extender is present, the effective phasevolume of the A block in the organic phase is represented by FormulaIII:

    %(vol.sub.a)=%(wt.sub.a)/D.sub.a /(%(wt.sub.a)/D.sub.a +%(wt.sub.b)/D.sub.b +%(wt.sub.d)/D.sub.d)                                     (III)

where:

%(wt_(d)) is the weight percent extender present, and

D_(d) is the density of the extender present.

For tapered block copolymers, the above numerator is further multipliedby a correction factor equal to 1--ι (where ι is the degree oftaperedness) to account for the isolated monovinylidene aromatic polymercontent. The degree of taperedness in the block copolymer is thepercentage of total monovinylidene aromatic monomer units that areisolated. Such isolated monovinylidene aromatic monomer units are thosesegments of monovinylidene aromatic monomer or oligomer units surroundedon both sides by conjugated diene monomer units and are easilydetermined by the use of nuclear magnetic resonance spectroscopy asdisclosed in Mochel, Rubber Chemistry and Technology, Vol. 40, p. 1200,1967. Because such isolated monomer or oligomer units do not contributesignificantly to the phase represented by the monovinylidene aromaticpolymer block, tapered block copolymers possess an effectivemonovinylidene aromatic polymer phase volume that is significantly lessthan the weight percent monovinylidene aromatic monomer content.

At lower monovinylidene aromatic monomer effective phase volumes,especially for polymers wherein the monovinylidene aromatic monomerblock molecular weight is relatively low, the tensile properties of theresulting films are unacceptably low. At higher monovinylidene aromaticmonomer effective phase volumes, the dispersion does not readily formfilms, especially at mild temperatures from about 25° C. to about 90° C.Moreover, films from such polymers require longer periods of time underannealing conditions and/or higher annealing temperatures to achievemaximum tensile strength properties. Such films are subject to polymerdegradation resulting in films possessing poor tensile properties,especially ultimate tensile strength.

Preferably, the weight average molecular weight (M_(w)) of the triblockblock copolymers is about 60,000 Daltons or greater, more preferably,about 76,000 Daltons or greater and most preferably, about 96,000Daltons or greater. Preferably, the weight average molecular weight(M_(w)) of the triblock block copolymers is 430,000 Daltons or less,more preferably, about 240,000 Daltons or less and most preferably,200,000 Daltons or less. In the embodiment where the block copolymer isa radial block copolymer, the weight average molecular weight ispreferably about 110,000 Daltons or more. In the embodiment where theblock copolymer is a radial block copolymer, the weight averagemolecular weight is preferably about 500,000 Daltons or less, morepreferably, 400,000 Daltons or less and most preferably, 300,000 Daltonsor less. Molecular weights are determined by size-exclusionchromatography. Commercially available polystyrene standards are usedfor calibration and the molecular weights of copolymers correctedaccording to Runyon et al., J. Applied Polymer Science, Vol. 13, p.2359, 1969, and Tung, L. H., J. Applied Polymer Science, Vol. 24, p.953, 1979.

Preferably, the B block of the block copolymers employed hereincomprises a high 1,4-content polymer of a conjugated diene. By this ismeant that the vinyl functionality of the resulting conjugated dienepolymer block is preferably below about 10 weight percent for blocks notcontaining butadiene or, in the case of blocks comprising butadiene,preferably below about 25 weight percent.

It is believed (but not agreeing to be bound by such belief) that whenthe monovinylidene aromatic polymer blocks possess the previously statedeffective phase volume, the monovinylidene aromatic polymer blockscoalesce, thereby causing the polymer matrix to possess a particulatedor spherical morphology instead of a cylindrical or lamellar morphology.Such morphology is desirable for the formation of films from dispersionshaving good strength properties and film formation rates. Suchmorphology, as well as the concept of polymer block phase volume, aredisclosed in S. L. Aggarwal, Block Polymers, Plenum Press, pp. 102-103,1970. It is further believed (but not agreeing to be bound by suchbelief) that the particulated or spherical morphology which is presentin the A block is the discontinuous phase which facilitates theformation of stable dispersions and strong films.

Block copolymers and techniques for their preparation are well known inthe art. Such polymers may be prepared by sequential anionicpolymerization utilizing alkyllithium initiators, such asn-butyl-lithium, sec-butyllithium, etc. They may also be prepared bycoupling of living block copolymers or by using soluble difunctionallithium initiators such as1,3-phenylene-bis(3-methyl-1-phenylpentylidene)-bis-(lithium), or asimilar initiator as disclosed in U.S. Pat. No. 4,196,154, the teachingsof which are incorporated herein by reference. The block copolymers maybe tapered or untapered. That is, the junction between the separateblocks may be gradual or abrupt. Untapered block copolymers may beformed by completely polymerizing each monomer component before addingthe next block-forming monomer to the reaction medium containing theliving polymer anion. Tapered block copolymers may be formed bycopolymerizing a mixture of the monomers using the previously mentioneddifunctional initiators. Due to the differing reactivities of themonomers, a relatively pure diene block initially forms, followed by anintermediate portion of such polymer containing increasing amounts ofinterspersed monovinylidene aromatic monomer or oligomers and, finally,a relatively pure monovinylidene aromatic polymer block.

After polymerization according to one of the foregoing anionicpolymerization techniques, the living polymer anion is terminated byaddition of a terminating agent containing a reactive hydrogen, orcoupled by a coupling agent containing multiple leaving groups. Suitableterminating agents include water, alcohols and carboxylic acids.Suitable coupling agents include ethylene dibromide, methylene chloride,carbon tetrachloride, silicon tetrachloride and dichlorodimethylsilane.Additional additives can be added to the reaction mixture before orafter the polymerization is completed for purposes of stabilizing thepolymer, preventing discoloration or for any other suitable purpose. Thepolymerization is normally conducted in an organic solvent such ashexane, toluene, cyclohexane, benzene or a mixture thereof.

Surfactants useful in the invention are those which emulsify the blockcopolymer(s) and optional extender in water. Anionic, cationic andnonionic surfactants may be used, with the anionic and cationicsurfactants being preferred. Even more preferred surfactants are theC₁₂₋₃₀ saturated and unsaturated carboxylic acids or salts thereof,sulfated alkylphenoxypoly(ethyleneoxy)ethanol alkali or ammonium saltsand dialkyl esters of alkali metal sulfosuccinic acid (for exampleAerosol™ OT dioctyl ester of sodium sulfosuccinic acid, available fromAmerican Cyanamid). Even more preferred are the C₁₂₋₃₀ saturated andunsaturated carboxylic acids or salts thereof. Preferred counterions arethe alkali metals and ammonium ions. Among the most preferredsurfactants are isostearic acid, linoleic acid, linolenic acid, lauricacid, oleic acid (for example, Industrene™ 105 oleic acid, availablefrom Humko Chemical), alkali metal salts of disproportionated rosin (forexample, Dresinate™ 214 potassium salt of disproportionated rosin,predominantly abietic acid). Preferably, the surfactants have an HLB ofabout 15 or greater and, more preferably, an HLB of about 18 or greater.

The surfactant is present in a sufficient amount to emulsify the blockcopolymer(s) and optional extender(s). If too much surfactant is used toprepare the aqueous dispersions, films prepared from the aqueousdispersions will not demonstrate the desired tensile properties. Thereason is that a significant amount of the surfactant will remain in thefilm which is formed from the aqueous dispersion. The maximum amount ofsurfactant useful is related to how much surfactant is retained in thefilm. More than this amount may be used if the excess portion is removedprior to film formation or can be leached from the film prior toannealing. Preferably, about 0.5 percent by weight or more of surfactantis present and more preferably, 1 percent by weight or more is present.Preferably, about 10 percent by weight or less surfactant is used, morepreferably, about 8 percent by weight is used and even more preferably,about 6 percent by weight or less is used. Where a portion of thesurfactant is removed prior to film formation, up to about 20 percent byweight may be used, provided no more than about 10 percent by weight ispresent in the final film.

To produce an aqueous dispersion (interchangeably referred to herein asa dispersion or a latex) the polymer, usually in the form of a solutionin an organic solvent, is dispersed in water using a suitable surfactantand the organic solvent is removed. One suitable procedure is previouslydisclosed in U.S. Pat. No. 3,238,173 (incorporated herein by reference).Emulsification can take place by any of the well-known means for thispurpose and the specific means utilized does not form an essentialaspect of the present invention. In one embodiment, the block copolymerand optional extender are dissolved in an organic solvent. In suchembodiment, a portion of the solvent is removed until the solids levelis preferably about 30 percent by weight or greater and, morepreferably, about 40 percent by weight or greater. Preferably, thesolids content is as high as possible. The upper limit is a practicalone, in that the solution must be processable. Preferably, the solidscontent is about 50 percent by weight or less. Thereafter, the blockcopolymer and optional extender are contacted with water and surfactantwith agitation to emulsify the mixture. Thereafter, the remainingsolvent is removed by conventional means, such as rotary evaporation orvacuum distillation. Preferably, the solids level is about 20 percent byweight or greater and more preferably, about 28 percent by weight orgreater. Preferably, the solids level is about 75 percent by weight orless, more preferably, about 70 percent by weight or less, even morepreferably, 65 percent by weight or less and most preferably, 60 percentby weight or less. Generally, the number average size of the resultinglatex particles is less than about 5.0 μM, more preferably, from about0.3 to about 2.0 μM. Preferably, the latex particles (the dispersedpolymer particles in the aqueous medium) are spherical in shape.

To prepare a film from the dispersion, a suitable form having a surfacein the shape of the desired resulting product (optionally having asurface coating of a suitable substance to promote film removal and/ordispersion deposition as previously known in the art) is coated with thedispersion and the water thereafter removed by evaporation. A preferreddispersion for use in the manufacture of dipped goods in the foregoingmanner contains about 20 percent by weight or greater of solids, morepreferably from about 25 percent by weight or greater and 27 percent byweight or greater. Preferably, the dispersion has a solid content ofabout 70 weight percent or less, more preferably, about 60 weightpercent or less and most preferably, 55 percent by weight or less. Asecond or further layer may be applied in the same manner to achievethicker films. The film resulting from the foregoing procedure may bedried and annealed, if desired, by any suitable technique, especially byheating. Preferable temperatures for drying and annealing are about 25°C. or greater, preferably, about 30° C. or greater and most preferably,about 50° C. or greater. Preferably, the temperatures for drying andannealing the films are about 130° C. or less, more preferably, from toabout 120° C. or less and most preferably, about 90° C. or less.Preferable times for drying and annealing are about 1 minute or greaterand more preferably, about 4 minutes or greater. Preferable times fordrying and annealing are about 10 hours or less, preferably, about 60minutes or less and more preferably, 30 minutes or less. At highertemperatures, shorter drying and annealing times are required. Thedrying and annealing steps of the process may be conductedsimultaneously or separately. For example, multiple film layers may bedeposited and dried before the resulting structure is annealed.

Preferably, the films are prepared by coagulation dipping techniques.Such techniques are well known in the art, see for example, Gazeley et.al., "Technological Processing of Natural Rubber Latex," Natural RubberScience and Technology, Chapter 4 (Ed. Roberts), Oxford University Press(1988) and Mausser, The Vanderbilt Latex Handbook, 3d. Ed., pp. 197-206,R. T. Vanderbilt Co., Inc. (1987), relevant parts incorporated herein byreference. In order to facilitate the preparation of a dispersion whichforms an acceptable film by coagulation, the surfactant must becarefully selected. The requirements for surfactants useful incoagulatable dispersions include: the ability to facilitate theformation of a stable dispersion, the formed dispersion must coagulatewhen exposed to divalent cations, such as calcium, the formed film mustexhibit acceptable wet gel strength, upon drying the film must becontinuous and the annealed film must meet the tensile strengthrequirements defined herein. Stable dispersions preferably exhibit thefollowing characteristics: after 168 hours of storage any particleswhich cream are redispersible and the dispersion is homogeneous afterredispersion, the particle size distribution (volume average) of thehomogeneous dispersion is essentially equivalent (changes less than 10percent) before and after storage and no visible sheen on the dispersionsurface appears after storage. A coagulatable dispersion preferablyproduces a solid mass of material when an equal volume of dispersion anda 10 weight percent calcium nitrate solution are contacted and theliquid phase remaining after coagulation is relatively clear. "Wet gel"as used herein means the solid material formed when the dispersion iscontacted with a solution containing a divalent cation salt. The wet gelpreferably contains the same solids content as the dispersion from whichit is formed. Wet gel strength can be measured according to thefollowing test. A uniform coating of a divalent cation, such as calciumnitrate, is applied to a test form in sufficient amount to coagulate awet gel film of the solids from the dispersion having a thickness ofabout 2 to about 20 mils (0.05 to 0.5 mm) thick. The form is preferablya glass jar of from about 2 inches (5.1 cm) to about 3 inches (7.6 cm)in diameter and at least about 2 inches (5.1 cm) high. Before the wetgel is dried, the form with the wet gel coated on it is submerged in astationary water bath and drawn through it at a rate of about 25 toabout 40 cm per second for a distance of at least 30 cm. This drawing isperformed on each coated form at least four times. The coating exhibitsacceptable wet gel strength if it remains intact with no delaminationfrom the form during the test.

Preferred surfactants for use in coagulatable dispersions include saltsof C₈₋₁₇ carboxylic acids having branching or cycloaliphatic moietiesand unsaturation in the carbon chain, C₁₈₋₃₀ carboxylic acids having inits carbon chain one or more of unsaturation, branching or acycloaliphatic moiety, and C₈₋₃₀ sulfosuccinic acid having a branchedcarbon chain, unsaturation in the carbon chain or a branched unsaturatedcarbon chain. More preferred coagulatable surfactants are salts ofC₁₈₋₃₀ carboxylic acids having in its carbon chain one or more ofcycloaliphatic moieties, unsaturation or branching and C₈₋₃₀sulfosuccinic acids having a branched carbon chain, unsaturation in thecarbon chain or a branched unsaturated carbon chain. Even more preferredcoagulatable surfactants include salts of C₁₈₋₃₀ carboxylic acids havingin its carbon chain one or more of unsaturation, branching or one ormore cycloaliphatic moieties. Among most preferred coagulatablesurfactants are oleic acid, abietic acid, isostearic acid, octadecanoicsulfosuccinic acid and ethylhexyl sulfosuccinic acid. The preferredcounterion of the salts are alkali metal or ammonium cations, with thesodium and potassium cations being the preferred counterions. Suchsurfactants are used in the amounts described hereinbefore.

Preferably, the films or elastomeric articles of the invention containan antiozonant which prevents or retards degradation due to ozoneattack. Preferably, the films or elastomeric articles which contain anantiozonant do not stain and do not have an unpleasant odor. Preferableantiozonants include dialkyl paraphenylenediamines, acetals andstyrene-substituted phenols. Preferred classes are the acetals andstyrene substituted phenols. A preferred dialkyl paraphenylene-diamineis N,N'-di-(2-octyl)p-phenylenediamine, available from R. T. Vanderbiltunder the trademark Antozite™ 1. A preferred acetal isbis-(1,2,3,6-tetrahydrobenzaldehyde)-pentaerythrityl acetal availablefrom Akrochem Corporation, under the trade name 70TBPA. A preferablestyrene-substituted phenol is bis-(alphamethylbenzyl)phenol, availableunder the trade name PRODOX™ 120 from PMC Specialties Group. Theantiozonants are used in a sufficient amount to render the films orarticles of the invention ozone resistant for a period of 1000 hours.Ozone resistance is determined according to the following test. Filmsaccording to the invention are cut into dumbbell shapes having thefollowing dimensions, 6.4 cm (length) by 1.3 cm (width) with a gaugedimension of 2.5 in. (6.4 cm) (length) by 0.5 in. (1.3 cm) (width). Thesamples are stretched to 100 percent elongation and secured to a hardsurface at such elongation and exposed to atmospheric ozone. The timefrom the start of the test until the samples break is the ozoneresistance. "Nonstaining" as used herein means transference of anoticeable color to white fiberboard during the ozone resistance test.Preferably, the antiozonant is present in an amount of 0.5 percent byweight or greater based on the article or film. Preferably, theantiozonant is present in an amount of 5 percent by weight or less basedon the weight of the film or article. The antiozonant can be blendedwith the block copolymer or organic phase in bulk, in solution or in thedispersion using techniques well known in the art. Preferably, theantiozonant is dissolved in an organic solvent and contacted with asolution of the block copolymer or organic phase. Preferably, the samesolvent is used for the antiozonant as the block copolymer or theorganic phase. Preferably, the solids level of the antiozonant is thesame as the solids level of the block copolymer or organic phase as thisfacilitates formation of a homogeneous mixture.

Preferably, the dispersions and films of the invention contain wax tofurther enhance the ozone resistance. Waxes useful in the films anddispersions of the invention include 1230 CP Hall No. Chek wax, MobileerC wax from Mobil Oil Corporation. Wax is preferably present in an amountof 0.5 percent by weight or greater based on the solids in thedispersion or of the film, more preferably, 1.0 percent by weight orgreater. Wax is preferably present in an amount of 5.0 percent by weightor less based on the solids in the dispersion or of the film, morepreferably, 4.5 percent by weight or less.

The film thickness is determined by the ultimate use. The desired filmthickness for the uses for which the films of the invention may be usedare well known in the art. Preferably, the films have a thickness ofabout 0.03 mm or greater, more preferably, 0.13 mm or greater and mostpreferably, about 0.20 mm or greater. Preferably, the films are about3.0 mm or less and, most preferably, about 0.30 mm or less. The films ofthis invention preferably exhibit a tensile strength at break of about11.0 MPa or greater after annealing at 80° C. for about about 30minutes. More preferably, the films exhibit a tensile strength of about16.5 MPa or greater and, most preferably, about 22 MPa or greater, whenannealed under such conditions.

Preferably, the films of this invention are free-standing, which meansthe films do not require a substrate to retain their integrity.

Films having adhesive properties may be prepared by incorporating asuitable tackifier, usually a low molecular weight organic polymer suchas a polyterpene or similar compound, in the film. Tackifying resinsuseful herein are those known in the art and include hydrogenated rosinesters, esters of polyhydric alcohols, phenol-aldehyde resins andhydrocarbon resins, which includes polyterpenes. U.S. Pat. No. 5,183,705provides a description of such tackifying resins, relevant portions areincorporated herein by reference. Additional formulants such as oils mayalso be added to modify the adhesive properties of the resulting film.Particularly useful oils are hydrocarbon oils, preferably paraffinic andnaphthenic oils. U.S. Pat. No. 3,935,338 discloses preferred oils usefulin adhesive formulations, relevant parts incorporated herein byreference. Such oils are preferably incorporated in amounts of 5 toabout 20 percent by weight of the final adhesive formulation. Thetackifiers and other formulants may be added to the polymer solution orincorporated into the latex. The resulting modified latex may be furtherconcentrated and coated onto a substrate, for example, a sheet or afilm, such as a masking tape backing. The substrate/film combination maythereafter be dried and, optionally, annealed to form the final product.

Having described the invention, the following examples are provided asfurther illustration and are not to be construed as limiting. Unlessstated to the contrary, parts and percentages are expressed on a weightbasis. Effective phase volumes were calculated using the previouslydisclosed Formulae (II and III). For such calculations, the densities ofthe respective polymers used were polystyrene: 1.047, polyisoprene:0.904 and polybutadiene: 1.01.

EXAMPLE 1 Films of Styrene-Isoprene-Styrene Block Copolymer

An aqueous dispersion was formed from a cyclohexane solution of astyrene-isoprene-styrene triblock copolymer having a total M_(w) of136,000 Daltons, and a styrene content of 14 weight percent and 12volume percent (effective phase volume). The surfactant used was Alipal™CO-436 sulfated nonylphenoxypoly-(ethyleneoxy) ethanol at a 3 percent byweight level. Molecular weights were determined by gel permeationchromatography using polystyrene standards and corrected for dienecontent. The polystyrene endblocks had weight average molecular weightsof 9500 Daltons. The total polyisoprene block M_(w) was 115,000 Daltons.The solvent was removed and the dispersion concentrated to 54 percentsolids by weight. Two-layer films were prepared by coating glass slideswith the latex, drying the films at room temperature to remove water andrepeating the process. The films were separated from the support and cutinto test specimens. The films were translucent and had a thickness ofabout 0.25 mm. Specimens were tested without annealing and afterannealing at 80° C. for the times identified in Table IA. Tensilestrengths were evaluated according to ASTM-D-412-80. Samples weredie-cut into dumbbell shapes having a gauge length of 25 mm and a widthof 3 mm. Cross-head speed was 50 cm per minute. Results are contained inTable IA.

                  TABLE IA                                                        ______________________________________                                        Strength as a Function of Annealing Time                                      ______________________________________                                        Minutes       0     2          8    16                                        Tensile Strength                                                                            0.9   16.9       20.2 20.3                                      at Break (MPa)                                                                ______________________________________                                    

Additional film samples were annealed at reduced temperatures. Resultsare contained in Table IB.

                  TABLE IB                                                        ______________________________________                                        Strength as a Function of Annealing Temperature-Time                          ______________________________________                                        Temp. (°C.)                                                                     40     40     50   50   60   60   70   70                            Time (min.)                                                                             4     16      4   16    4   16    4   16                            Tensile  1.9    3.7    4.1  9.9  7.8  18.1 17.2 18.8                          Strength                                                                      at Break                                                                      (MPa)                                                                         ______________________________________                                    

As may be seen by reference to the results of Tables IA and IB, filmshaving good tensile strength properties, as indicated by tensilestrength at break values, can be formed according to the presentinvention without the use of additives such as additional copolymerlatices or aliphatic solvents even at relatively low annealingtemperatures from 40° C. to 80° C.

Comparative A

Films of Block Copolymer Having Relatively Long Polystyrene EndblockLength

A dispersion was made from a styrene-isoprene-styrene block copolymerhaving M_(w) of 205,000 Daltons and having a styrene content of 15weight percent and 13 volume percent. The polystyrene endblocks hadmolecular weights of 15,300 Daltons. The polyisoprene centerblockmolecular weight was 174,000 Daltons. The dispersion used in making thefilms had a solids content of 54 weight percent. The films were annealedat 80° C. for the times identified in Table II. Film formation andtesting were according to the techniques of Example 1. Results arecontained in Table II.

                  TABLE II                                                        ______________________________________                                        Strength as a Function of Annealing Time                                      ______________________________________                                        Minutes      0       16     60   120  240                                     Tensile Strength                                                                           0.2     1.6    5.4  8.5  9.4                                     at Break (MPa)                                                                ______________________________________                                    

Compared to the results of Table I, it may be seen that block copolymershaving a longer endblock vinyl aromatic polymer length require longerannealing times and/or higher annealing temperatures to achieve maximumtensile strengths.

Comparative B

Films of Block Copolymer Having Relatively Short Endblock Length

A dispersion of a styrene-isoprene-styrene block copolymer was preparedas in Example 1. The triblock copolymer had a M_(w) of 85,000 Daltonsand had a styrene content of 16 weight percent and 15 volume percent.The polystyrene endblock molecular weight was 6800 Daltons. Thepolyisoprene block molecular weight was 71,000 Daltons. Film sampleswere prepared by deposition onto glass and annealed at 80° C., as inExample 1. Results are contained in Table III.

                  TABLE III                                                       ______________________________________                                        Strength as a Function of Annealing Time                                      ______________________________________                                        Minutes       0     4          16   120                                       Tensile Strength                                                                            1.4   5.0        6.7  7.5                                       at Break (MPa)                                                                ______________________________________                                    

By comparison with the results of Table I, it may be seen that arelatively short endblock vinyl aromatic polymer length gives blockcopolymers having rapid annealing times, but tensile strength propertiesmay be reduced. By controlling the length of the monovinylidene aromaticblock, it is possible to maximize the tensile strength of the blockcopolymer and minimize the annealing time and temperature requirements.

EXAMPLE 2 Films of Radial Block Copolymer

A dispersion of a four-armed styrene-isoprene block copolymer coupledwith silicon tetrachloride was prepared as in Example 1. The polymer hadan apparent molecular weight by gel permeation chromatography (GPC) of227,000 Daltons. The styrene content was 15 weight percent, 13.2 volumepercent. The polystyrene endblock weight average molecular weight was11,300 Daltons. The polyisoprene radial block apparent weight averagemolecular weight was 182,000 Daltons. Film samples were prepared bydeposition onto glass and annealed and tested as in Example 1. Resultsare combined in Table IV.

                  TABLE IV                                                        ______________________________________                                        Strength as a Function of Annealing Time                                      ______________________________________                                        Minutes       0     4          16   60                                        Tensile Strength                                                                            1.4   14.9       19.1 21.0                                      at Break (MPa)                                                                ______________________________________                                    

EXAMPLE 3 Films of a Tapered Block Copolymer

Films of a symmetrically tapered styrene-isoprene-styrene blockcopolymer containing 26 weight percent styrene, an overall molecularweight (M_(w)) of 228,000 Daltons, a measured isolated styrene of 52percent and effective phase volume styrene content of approximately 11percent were prepared as in Example 1. The polystyrene endblockmolecular weight was measured by degradation analysis and GPC to be 9700Daltons. Films were cast on glass slides, dried at room temperature andannealed as in Example 1. Strength properties were tested according toASTM-D-412 after annealing at 80° C. and at various temperatures.Results are contained in Tables VA and VB.

                  TABLE VA                                                        ______________________________________                                        Strength as a Function of Annealing Time                                      ______________________________________                                        Minutes       0     4          16   30                                        Tensile Strength                                                                            0.5   4.8        11.8 13.1                                      at Break (MPa)                                                                ______________________________________                                    

                  TABLE VB                                                        ______________________________________                                        Strength as a Function of Annealing Temperature-Time                          ______________________________________                                        Temp. (°C.)                                                                     60     60     70   70   80   80   90   90                            Time (min.)                                                                             4     30      4   30    4   30    4   30                            Tensile  1.1    2.9    2.0  5.3  4.8  13.1 10.6 18.1                          Strength                                                                      at Break                                                                      (MPa)                                                                         ______________________________________                                    

Comparative C

Films of a Triblock Copolymer Having High Polystyrene Volume Percent

Dispersions were prepared from a toluene solution of astyrene-butadiene-styrene triblock copolymer. The polymer weight averagemolecular weight was approximately 100,000 Daltons. The polystyrenecontent was 30 weight percent, 29 volume percent. The polystyreneendblock molecular weight was 15,000 Daltons. The polybutadiene blockmolecular weight was 70,000 Daltons. When cast onto a clean glass plateaccording to Example 1, severe cracking of the film occurred. Nocoherent film could be formed at room temperature.

Comparative D

A dispersion was prepared from a cyclohexane solution of Kraton™ 1111styrene-isoprene-styrene block copolymer containing nominally 22.7percent styrene having a molecular weight of 147,000 Daltons and styreneendblock molecular weight of 16,700 Daltons. The film was annealed at80° C. for various times and the results are compiled in Table VI.

                  TABLE VI                                                        ______________________________________                                        Time at 80° C.                                                                      0      4          16   60                                        (min.)                                                                        TS at Break  0.35   1.90       4.96 11.6                                      (MPa)                                                                         ______________________________________                                    

EXAMPLE 4

To a cyclohexane solution of the block copolymer described inComparative C was added 44 percent by weight based on the blockcopolymer of an aliphatic mineral oil. This blend was dispersed in wateras described in Example 1 and the cyclohexane was removed bydistillation. The styrene phase volume in the organic phase wascalculated to be 19 percent based on the assumption that all of themineral oil is contained in the butadiene phase. The dispersion was caston a clean glass plate which, upon drying, left a coherent film. Thefilm was annealed in a forced-air oven at 80° C. Samples were tested fortensile strength after varied annealing times. The results are compiledin Table VII.

                  TABLE VII                                                       ______________________________________                                        Time at 80° C.                                                                       4     16         30   60                                        (min.)                                                                        Tensile Strength                                                                            1.7   10.1       11.6 11.7                                      (MPa)                                                                         ______________________________________                                    

EXAMPLE 5

A dispersion was made from a cyclohexane solution containing 35 percentby weight of a styrene-isoprene-styrene block copolymer containing 18percent by weight polystyrene (15.9 volume percent) with the structurepolystyrene-polyisoprene-polystyrene being 10,000-110,000-10,000. Thissolution was dispersed into water using Alipal™ CO-436 surfactant at alevel of 3.0 percent by weight based on polymer solids. After thedispersion was formed, the solvent was removed under vacuum to give adispersion that was 59 percent by weight solids. Films were cast ontoglass plates in two layers and dried 2-16 hours at room temperature toprovide a dried film thickness of approximately 0.25 mm. These filmswere cut into samples, annealed at 80° C. for various times and testedaccording to ASTM-D-412. The results are compiled in Table VIII.

                  TABLE VIII                                                      ______________________________________                                        Annealing Time                                                                              0     2          8    16                                        at 80° C. (min.)                                                       TS at break   .57   3.23       11.5 13.5                                      (MPa)                                                                         ______________________________________                                    

EXAMPLE 6

A dispersion of styrene-isoprene-styrene block copolymers was preparedas in Example 1. Polymer A was 14 weight percent styrene (12.4 volumepercent styrene) with a structure polystyrene-polyisoprene-polystyreneof 9500-109,000-9500. Polymer B was 15 weight percent styrene (13.2volume percent styrene) with a structurepolystyrene-polyisoprene-polystyrene of 15,300-154,400-15,300. Filmsamples were prepared on glass and annealed as described in Example 1.The results are compiled in Table IXA.

                  TABLE IXA                                                       ______________________________________                                        Annealing Time                                                                              0     2          8    16                                        at 80° C. (min.)                                                       Sample A      .90   16.9       20.2 20.3                                      Sample B      .21   --         .81  1.55                                      ______________________________________                                    

Sample A was annealed at temperatures below 70° C. Strength after 4 and16 minutes was noted. The results are compiled in Table IXB.

                  TABLE IXB                                                       ______________________________________                                        Temperature (°C.)                                                                  70        60     55     50  40                                    Strength 4 min.                                                                           17.2      7.8    6.9    4.1 1.86                                  Strength 16 min.                                                                          18.8      18.1   19.9   9.9 3.7                                   ______________________________________                                    

EXAMPLE 7

A dispersion was prepared from a cyclohexane solution of astyrene-butadiene-styrene triblock copolymer containing 17 weightpercent styrene having a molecular weight of 145,000 Daltons. Thiscorresponds to 16.5 volume percent styrene. The molecular weight of thepolystyrene endblocks was 12,300 Daltons. After drying at roomtemperature, samples of the film were annealed in a forced-air oven at80° C. for various times. The results are compiled in Table X.

                  TABLE X                                                         ______________________________________                                        Time at 80° C.                                                                       4     16         60   300                                       (min.)                                                                        Strength (MPa)                                                                              3.4   11.7       12.0 21.2                                      ______________________________________                                    

EXAMPLE 8

Dispersions were prepared from both toluene and cyclohexane solutions ofa styrene-isoprene-styrene triblock copolymer containing 15 weightpercent styrene. This corresponds to 13.2 volume percent styrene. Afterdrying at room temperature, samples were annealed in a forced-air ovenat 80° C. for various times. This shows that either aliphatic oraromatic solvents may be used to prepare dispersions which anneal tohigh strengths. The results are compiled in Table XI.

                  TABLE XI                                                        ______________________________________                                        Time at 80° C.                                                                      2      8          30   60                                        Toluene      12.9   18.3       20.5 21.1                                      Cyclohexane   8.0   13.2       17.9 19.9                                      ______________________________________                                    

EXAMPLE 9

A styrene-butadiene-styrene triblock copolymer (SBS) was dissolved intocyclohexane to produce a 16 percent by weight solids solution. Themolecular composition of the SBS polymer was 18.4 percent styrene and84,000 peak molecular weight. This SBS stock solution was emulsifiedusing a Silverson Model L4R high shear mixer, batchwise. The batchcomposition is 2750 grams of polymer solution (440 grams of polymer),23.2 grams of surfactant (dioctylsulfosuccinic acid sodium salt) and1294 grams of water. The three components are mixed at maximum rpm(nominally 5000 rpm) for 5 minutes. During the mixing step, 0.6 ml of adefoamer is added to prevent excessive foaming. Solvent removal isaccomplished by vacuum devolatilization in a rotating glass apparatuswith a bath temperature of 90° C. The finished sample, after filtering,was analyzed at 25.4 percent solids and was added to an agitated tank.The agitation was sufficient to mix the solution but does not introduceany air bubbles into the sample. A glass mold at 90° C. with a slightlyroughened surface was dipped into a calcium nitrate and methanolsolution (nominally 10 percent solids) and allowed to cool to roomtemperature. The mold was dipped into the sample with a dwell time of 5seconds and removed and placed for a minimum of 5 minutes into a watertank which was maintained at 40° C. The wet film was dried and annealedin a forced-air oven at 90° C. for 20 minutes and then removed andtested. The film was free of any holes and possessed a tensile strengthof greater than 3000 psi tensile.

EXAMPLE 10

A styrene-isoprene-styrene (SIS) triblock copolymer was dissolved intocyclohexane to form a 16 percent by weight solids solution. Thissolution was emulsified using a Silverson Model L4R high shear mixer.The batch consists of 800 grams of SIS stock solution 128 grams polymer,512 grams of water and 6.8 grams of a surfactant anddioctylsulfosuccinic acid sodium salt. The mixture was mixed at 5000 rpmfor 5 minutes. During the mixing step 0.3 ml of a defoamer is added toprevent excessive foaming. Solvent removal is accomplished by vacuumdevolatilization in a rotating glass apparatus with a bath temperatureof 90° C. The finished dispersion after filtration having a solids levelof 27 percent by weight was added to an agitated tank. Agitation wassufficient to mix the dispersion but not to introduce air bubbles to themixture. A glass mold at 90° C. having a lightly roughened surface wasdipped into a calcium nitrate and methanol solution (about 10 percent byweight solids) and allowed to cool to room temperature. The mold wasdipped into the dispersion for about 5 seconds and removed. The coatedmold was placed in a water tank at 40° C. for about 5 minutes. The wetfilm was dried and annealed in a forced-air oven at 90° C. for 20minutes and then removed and tested. The film was free of any holes andpossessed a tensile strength of greater than 3000 psi (20.7 MPa).

EXAMPLES 11-16

Dispersions were prepared using the process described in Example 10 withthe exception that different surfactants were used. The surfactants weresodium salt of abietic acid, potassium salt of abietic acid, sodium saltof oleic acid, potassium salt of oleic acid, sodium salt of 2-ethylhexylsulfosuccinic acid and sodium salt of dioctylsulfosuccinic acid. Theresulting films were tested for dispersion stability, ability tocoagulate, wet gel strength and examined for film uniformity and tensilestrengths after annealing. All of the films passed the tests anddemonstrated tensile strengths of greater than 20.7 MPa (3000 psi) afterannealing for 30 minutes at 80° C.

EXAMPLE 17

188 Grams of triblock styrene-isoprene-styrene having 18 percent byweight styrene and a peak average molecular weight of 125,000 Daltons,available from Dexco Polymers under the trademark and designationVECTOR™ 4111, 584 grams of cyclohexane, 5.8 grams of a sodium saltsolution of oleic acid, 3.8 grams of N,N'-di-2-octylparaphenylenediamine available from R. L. Vanderbilt under the tradename and designation ANTOZITE™ 1, 3.8 grams of CP HALL™ 1230 paraffinwax (MP 3501 wax) and 0.8 grams of butyl hydroxy toluene (BHT) wereblended together. The blend was contacted with 368 grams of water in ahigh shear mixer and mixed at 5000 rpm for 10 minutes. The dispersionwas transferred to a heated rotating glass bulb to remove the solvent togive a dispersion of 42 percent by weight solids. Films of thedispersion were prepared by coagulation as described in Example 10. Thefilms had thicknesses of about 7 mils (0.18 mm). Specimens were cut fromthe films using a 2.5 in. × 0.5 in. (6.4×1.3 cm) ASTM "L" tensile die.The thin portion of the specimens were stretched to 100 percentelongation and secured in place to a stiff white fiberboard. The sampleswere exposed to ambient ozone levels (between 1 and 5 parts per hundredmillion (pphm)). Time to break was recorded to within 24 hours. Thefilms were reddish-brown in color, were nonstaining and exhibited anozone resistance of greater than 1000 hours.

EXAMPLE 18

Example 17 was repeated except the antiozonant used wasbis-(1,2,3,6-tetrahydrobenzaldehyde)-pentaerythrityl acetal in an amountof 5.0 grams (3.0 parts per hundred parts of resin (phr)). The film wasnonstaining and exhibited an ozone resistance of greater than 1000hours.

EXAMPLE 19

Example 17 was repeated, except the antiozonant used was abis-(alphamethylbenzyl)phenol available from PMC Specialties Group underthe trade name and designation PRODOX™ 120 in an amount of 5.0 grams(3.0 phr). The film was white and nonstaining and exhibited an ozoneresistance of greater than 1000 hours.

What is claimed is:
 1. An aqueous dispersion which is capable of forminga free-standing, coherent, elastomatic, solid film which, after dryingand annealing at 80° C. for 30 minutes, demonstrates a tensile strengthof about 11.0 MPa or greater wherein the dispersion comprises:I. anorganic phase comprising one or more block copolymer(s) corresponding tothe formula:

    A-B-X.sub.m -(B-A).sub.n

wherein each A is a polymer block consisting essentially of amonovinylidene aromatic monomer, each B is a polymer block consistingessentially of a conjugated diene and, optionally, a monovinylidenearomatic monomer, X is the remnant of a multifunctional coupling agent,m is 0 or 1, and n is an integer from 1 to 5, each monovinylidenearomatic monomer block having a weight average molecular weight fromabout 8,000 to about 15,000 Daltons, each conjugated diene black havinga weight average molecular weight from about 30,000 to about 200,000Daltons; II. a surfactant in sufficient amount to emulsify the organicphase and such that a film formed from the dispersion exhibits therequited properties; and III. water,wherein the effective phase volumeof the A block in the organic phase is from about 5 to about 20 volumepercent.
 2. A dispersion according to claim 1 wherein the surfactant ispresent in an amount of from about 0.5 to about 10 percent by weight. 3.A dispersion according to claim 2 wherein the monovinylidene aromaticmonomer is styrene and the conjugated diene is 1,3-butadiene orisoprene.
 4. A dispersion according to claim 3 wherein the weightaverage molecular weight of the one or more block copolymers is fromabout 76,000 to about 240,000 Daltons.
 5. A dispersion according toclaim 4 wherein the organic phase further comprises an extendercomprising a hydrocarbon oil or a polymer compatible with the B block ofthe copolymer.
 6. A dispersion according to claim 5 wherein theeffective phase volume of the monovinylidene aromatic polymer blocks isfrom about 10 to about 19 percent.
 7. A dispersion according to claim 6wherein the surfactant is a C₁₂₋₃₀ carboxylic acid or salt thereofhaving an HLB of about 15 or greater.
 8. A dispersion according to claim4 wherein the organic phase comprises two or more block copolymerswherein the average A block content of the two or more block copolymersis from about 5 to about 25 percent by weight and wherein themonovinylidene aromatic monomer block of each of the two or more blockcopolymers has a weight average molecular weight of from about 8,000 toabout 15,000 Daltons.
 9. A dispersion according to claim 8 wherein theeffective phase volume of the monovinylidene aromatic polymer blocks isfrom about 12 to about 18 percent.
 10. A dispersion according to claim 9wherein the surfactant is a C₁₂₋₃₀ carboxylic acid or salt thereofhaving an HLB of about 15 or greater.
 11. A dispersion according toclaim 1 wherein the organic phase further comprises an antiozonant. 12.A dispersion according to claim 11 wherein the antiozonant is selectedfrom the group of dialkyl paraphenylenediamines, acetals andstyrene-substituted phenols.
 13. A dispersion according to claim 12wherein the antiozonant is selected from the group of acetals andstyrene-substituted phenols.
 14. A dispersion according to claim 12wherein the antiozonant is selected from the group of N,N'-di-2-octylparaphenylenediamine,bis-(1,2,3,6-tetrahydrobenzaldehyde)-pentaerythrityl acetal andbis-(alphamethylbenzyl)phenol.
 15. A dispersion according to claim 12wherein the organic phase comprises from about 0.5 to about 5 percent byweight of antiozonant based on the solids in the dispersion.
 16. Adispersion according to claim 12 wherein the organic phase comprisesfrom about 3 to about 5 percent by weight of antiozonant based on thesolids in the dispersion.
 17. A dispersion according to claim 12 whereinthe surfactant is selected from salts of C₈₋₁₇ carboxylic acids havingbranching or cycloaliphatic moieties and unsaturation in the carbonchain, C₁₈₋₃₀ carboxylic acids having in its carbon chain one or more ofcycloaliphatic moieties, unsaturation or branching and C₈₋₃₀sulfosuccinic acids having one or more of unsaturation and branching inits carbon chain.
 18. A dispersion according to claim 17 wherein thesurfactant is selected from the group of salts of C₁₈₋₃₀ carboxylicacids having in its carbon chain one or more of unsaturation, branchingor one or more cycloaliphatic moieties and C₈₋₃₀ sulfosuccinic acidshaving one or more of a branching and unsaturation in the carbon chain.19. A dispersion according to claim 17 wherein the surfactant isselected from the group of salts of oleic acid, abietic acid, isostearicacid, octadecanoic sulfosuccinic acid and ethylhexyl sulfosuccinic acid.20. A dispersion according to claim 12 which further comprises a wax.21. A dispersion according to claim 1 which further comprises atackifier.